1 Monster

From DoomWiki.org

1 Monster (called 1 Monster Megawad in its text file) is a 2007 megawad featuring 25 maps created by 15 Doomworld community members. It requires a Boom-compatible source port to play. As the name would imply, each map contains just one type of monster.

The development of the project occurred entirely within one Doomworld thread started by Dr. Zin. However, following its review in The /newstuff Chronicles #311, he wrote a post implying that he did not consider the megawad's concept a good one in the first place [1].